Reply to: Arguments for a comet as cause of the Hopewell airburst are unsubstantiated

We would like to thank Neuhäuser and Neuhäuser 1 for their critical review of our paper 2 . We presented multi-proxy evidence of an airburst event, which occurred in the Ohio River valley 1699–1567 years ago (252–383 CE). Support for the occurrence of an airburst event includes a disruption in vegetation, meteorites, micrometeorites, and positive anomalies of iridium and platinum in radiocarbon dated, charcoal-rich, Hopewell habitation strata. Our suggestion that the airburst was the result of a comet fragment was based on the overlap of proxies from the Ohio River valley and those recovered from KT boundary, YD boundary, and the Tunguska airburst event sites, which have been attributed to the airburst of comet fragments 2–5 . Neuhäuser and Neuhäuser’s 1 commentary raises an important question, What proxies are needed to trace the origin of ancient impactors on the Earth? Ancient airburst events from comet fragments and asteroids are difficult to accurately trace. We recognize that asteroids are the parent bodies of chondrites, and they are physi-cally and chemically distinct from comets. Neuhäuser and Neuhäuser 1 provide substantial theoretical evidence that the Hopewell impactor could not have been a comet fragment. Based on their observations, we concede that the Hopewell airburst was more likely the result of an asteroid exploding in the upper atmosphere, an interpretation, which is more in alignment with current interpretations of the KT boundary,

www.nature.com/scientificreports/ Neuhäuser and Neuhäuser 1 objected to our use of Native American oral histories and they generate alternative and varied interpretations for each tradition. Native American symbol systems and oral histories are observations and should not be dismissed as local tales. Rather, they depict an atmospheric phenomenon associated with the airburst. Descendant tribes of the Hopewell have oral histories of a singular event and we are of the opinion that they accurately portray a cosmic airburst.
Native Americans are keen observers of celestial bodies and their relationships with humans and the natural world. Their astronomical knowledge has been passed down over thousands of years as oral histories and symbolically represented in art, communal ceremonies, dance, songs, storytelling, and rituals [13][14][15] . Different Native American tribes have different names for the same symbolic creature (Cherokee-Uktenah, Haudenosaunee-Dajoji, Myaamia-Lenipinšia, Shawnee-Tekoomsē), a horned serpent known as the Sky Panther, a creature that appears at the time of cosmic chaos 20 .
Neuhäuser and Neuhäuser 1 state that Tekoomsē is a reference to "shooting stars" rather than a comet. They use a non-Native American spelling of Tekoomsē (i.e., Tecumseh) and state that there are multiple intepretations of his name. Changes in Native American names occur with changes in a person's life 20 . In Algonquian, Tekoomsē means "blazing comet" 21 . The name Tekoomsē, Sky Panther, was given in 1769, within the first year of his life, when comet C/1769 P1 was visible to the naked eye 21 . It is also noteworthy that comet C/1811 F1 is known as "Tecumseh's Comet" 22 . Tekoomsē believed the comet was a good sign for intertribal unification 21,22 . We also find it significant that multiple Hopewell images of the Sky Panther (horned serpent) were found at the epicenter of the airburst and in direct association with a pallasite (Fig. 2) 20,23 .
Neuhäuser and Neuhäuser 1 raised the issue that Hopewell people traded meteorites. This suggestion was first positied in 1882 by Charles Louis Metz and Frederick Ward Putnam 20,23 . In 1882, Metz found the first pallasites at the Turner site, and that same year, the Brenham pallasite strewn field was discovered in Kiowa County, Kansas 24 . Because pallasites are a rare form of stony-iron meteorites, and they comprise a very small percentage of all meteorites, Metz and Putnuam presumed that the Turner site specimens had been collected from the recently discovered Brenham strewn field 20,24 .  www.nature.com/scientificreports/ Native Americans have traded exotic materials across more than 2000 km since the late Pleistocene 25 . Octahedrites and pallasites contain ductile and malleable nickel and iron. Thus, we would expect meteorites to have been valuable trade items throughout the region for more than 15,000 years. Instead, we find meteorites temporally restricted to the Hopewell cultural complex, ~ 250-380 CE. Furthermore, pallasites < 2.5 mm in diameter from the epicenter of the airburst cannot be explained as trade items 2 . Also, the concentrations of Ga and Ge in the Ohio River valley pallasites are 10% lower than the Brenham pallasites and Pt is five times lower 2 .
Neuhäuser and Neuhäuser 1 suggest that the Hopewell airburst could have been produced by a small meteorite. However, a meteoritic airburst cannot explain the co-occurrence of both octahedrites and pallasites. Likewise, it does not explain the descendant Native American oral histories and earthwork symbolism. There will always be some degree of ambiguity in explaining the cause of ancient airburst events and tracing the origin of ancient impactors on the Earth. While we agree with Neuhäuser and Neuhäuser's 1 arguments that the Hopewell airburst event was likely the result of an asteroid rather than a comet, their suggestion of a meteoritic airburst is not persuasive.

Data availability
No datasets were generated or analyzed during the current study, others than those published in Tankersley et al. 2 .